1. Field of the Invention
The present invention relates to a detection apparatus for detecting a lane marking on a road, and more particularly to an on-vehicle detection apparatus for detecting the lane marking based on road-surface images detected from an area in front of the vehicle.
2. Description of the Related Art
Conventionally, there have been disclosed detection apparatuses capable of detecting the lane marking on the road based on an image-processing result processed from detected road-surface images from an area in front of the vehicle. The lane marking is referred to as a line on the road which is used to differentiate traffic lanes for running vehicles. The lane marking is generally produced as a white line consisting of a dotted line and a solid line, or a raised road marker placed along a traffic lane at constant intervals.
The detection apparatus is configured to extract edge points showing the white line or the raised road markers on the road and to detect the lane marking based on a plurality of extracted edges. The detected lane marking in combination with vehicle-information such as velocity, running direction and steering angle is used to detect any departure from the traffic lane. Also, the detected lane marking and such information can be used for automatic steering control of the vehicle.
When the painted length of the lane marking is short so that the intervals between the lane marking are long, or raised road markers only are used to separate the lanes, it is considered that the image of the lane marking does not match a frame of the image to be processed so that the lane marking may not be recognized by the detection apparatus properly. That is, an accuracy to detect the lane marking (detection accuracy) may be decreased. Specifically, when the detection accuracy is decreased and if the vehicle is departing from the lane, necessary alert (e.g. departure alert) to the driver on vehicle may not be performed appropriately. Further, some of vehicle-control functions may be affected by the decreased detection accuracy.
In this regard, to solve the above-described problem, for instance, a Japanese patent application laid-open publication No. 2006-350571 discloses a lane-marking detection apparatus in which the lane marking is detected from the latest image combined with previous images which have been acquired. This detection apparatus is designed in order to enhance the detection accuracy of the lane marking by increasing the number of objects of the lane marking (i.e., the number of edge points).
The detection apparatus disclosed in the foregoing publication is configured to extract the edge points from image data taken by on-vehicle camera and to generate linear-shape edge lines (i.e., lane markings) by appropriately linking the respective edges. However, the detection apparatus is designed to combine the frames only when the linear-shape edge line cannot be generated from edges of an acquired single frame. When the number of extracted edges is not enough to generate the edge line, but the linear-shape edge is generated successfully, the frames are not combined. In this case, since the linear-shape edge line is generated based on lower extracted edges than desirable number of edges, detection accuracy may be decreased.